1. Field of the Invention
The invention relates to an oil pump constructed as gear ring pump for reciprocating piston internal-combustion engines and automatic transmissions. In particular, the invention relates to such an oil pump for the engines and automatic transmissions of motor vehicles.
2. Description of the Prior Art
In engines, the pump normally serves to supply the engine with lubricating oil whilst in transmissions it normally supplies them with hydraulic oil for actuating the switching elements but also with oil for cooling the hydrodynamic converter and with lubricating oil for the gears. The pump housing can be flanged directly to the aggregate housing. In the aforementioned automatic transmissions the transmission input shaft may also be formed as part of the rotating converter housing. The formation of the oil pump as gear ring pump, the pinion of which is mounted directly on the main shaft of the aggregate, has many advantages. In particular, it is very simple in construction and avoids separate drive elements for a separately arranged oil pump. However, this essential advantage is offset by the disadvantage that in the internal-combustion engines and transmissions mentioned the main shafts execute considerable transverse displacements in operation due to the greatly changing operating conditions. Thus, the radial play which the centre of the crankshaft of the engine of an automobile executes is of the order of magnitude of 0.1 to 0.2 mm.
The result of this is that the pinion of the gear ring pump mounted on the shaft must also follow most of the centre displacement of the shaft. Since the hollow gear is practically always mounted in a separate housing which is screwed to the engine and transmission housing, additional radial shifts also occur so that the deviations of the desired position add up and in total may amount to several tenths of a millimeter. If the tooth play between pinion and hollow gear is made large enough to take up all these errors in the meshing play without constraints and inadmissible large loads destroying the toothing, this results in substantial disadvantages. Firstly, the sealing between the working chambers will no longer suffice for the delivery pressure. In particular at low speeds of rotation of the engine or the transmission the volumetric efficiency of the pump plays a major part and depends in particular in the gear ring pump on the tooth flank play. It should be remembered here that in the pumps improved by the invention, in which the hollow gear has only one tooth more than the pinion, all the teeth of the pinion and of the hollow gear are to be continuously in engagement with each other. The demand for high tooth play for compensating the pinion shifts leads therefore also to a very high play not only between the driving tooth flanks but also between the sealing tooth heads. This leads necessarily to a considerable impairment of the volumetric efficiency.
Since of course relatively little energy is necessary to generate noises, gears with large tooth play tend to hammer against each other, particularly when unsteady movement states are present as is the case in the gear ring pumps improved by the invention. In particular, in crankshafts of motor vehicles such unsteady movements are present not only in the radial direction but also in the peripheral direction so that a combination of translational and rotational oscillations occurs which is transmitted almost completely to the pinion. Since the hollow gear follows its own dynamic laws of motion, knocking sounds arise with large tooth pay which today cannot be considered acceptable.
In the gear pumps used today of the type outlined at the beginning, as a rule the tooth form of the one gear is defined by rolling on the tooth form of the other gear, this requiring of course a predetermined axial spacing. With a large tooth play, and this is necessary unless other precautions are taken, these generation conditions are no longer present so that the requirement for constant rotation angle transmission ratio in every relative angular position is no longer fulfilled. These errors also then generate accelerations and decelerations which manifest themselves as knocking.
Attempts have been made to master these problems by not only making the tooth play large but also the bearing play of the hollow gear in its housing. However, this not only likewise leads to noises but also to rapid wear of the toothing. Moreover, the tooth flank forms hitherto employed, which were usually defined as relatively easily calculatable and produceable arcs and trochoids, have unfavourable engagement angles, radii of curvature which are too small at the engagement points and poor or even no engagement relationships in the tooth bottom. If the pinion is mounted in the pump housing with a collar this increases the length of the engine or the transmission and adds to the constructional expenditure.